The invention relates to a process for producing a crystalline silicon thin film (layer). More particularly, the invention relates to a process for producing a crystalline silicon thin film, which enables, for example, the temperature required in the production process of a crystalline silicon thin film to be lowered to keep the quality of the crystalline silicon thin film, can realize close control of a steep dopant concentration gradient and the like, and can produce a crystalline silicon thin film suitable for an increase in fabrication density and a reduction in layer thickness of semiconductor devices.
A crystalline silicon thin film formed on a dissimilar substrate such as glass (this structure being called SOI (silicon-on-insulator)) has many advantageous properties, such as easy separation between semiconductor devices, higher integration density, lower power consumption, and higher speed.
A conventional production process of this type of crystalline silicon thin film comprises the steps of: anodically converting the surface of a crystalline silicon semiconductor substrate to a porous silicon layer; forming a crystalline silicon thin film on the porous silicon layer by epitaxial growth; and finally separating and removing the crystalline silicon semiconductor substrate, together with the porous silicon layer that is the crystalline silicon semiconductor substrate in its portion which has been rendered porous, from the crystalline silicon thin film joined to a support substrate (Japanese Patent No. 2962918 and Japanese Patent Laid-open No. 79330/1998). This production process has the following advantage. In this production process, a porous silicon layer, of which the pore diameter can be easily regulated by anodic conversion conditions, is used as a release layer. Therefore, a multi-layer structure comprising a plurality of layers having different functions (for example, a porous layer having smaller-diameter pores as an epitaxially grown adherent layer and a porous layer having larger-diameter pores as a release layer) can be easily formed, and this enables the crystalline silicon thin film to be simply and surely produced.
Since, however, a monocrystalline silicon thin film is formed by epitaxial growth which requires a high-temperature atmosphere of about 1000xc2x0 C., this production process poses problems including that the film quality lowers with increasing the fabrication density of semiconductor devices and reducing the film thickness and, further, it is difficult to closely regulate a steep dopant concentration gradient and the like.
Accordingly, it is an object of the invention to provide a process for producing a crystalline silicon thin film, which enables, for example, the temperature required in the production process of a crystalline silicon thin film to be lowered to improve the quality of the crystalline silicon thin film, can realize close control of a steep dopant concentration gradient and the like, and can produce a crystalline silicon thin film suitable for an increase in fabrication density and a reduction in layer thickness of semiconductor devices.
The above object can be attained by the following production processes of a crystalline silicon thin film.
[1] A process for producing a crystalline silicon thin film, comprising the steps of:
rendering at least a part of the surface of a crystalline silicon semiconductor substrate porous to convert at least a part of the surface of the crystalline silicon semiconductor substrate to a porous silicon layer;
forming a catalytic metal layer on the porous silicon layer;
forming an amorphous silicon thin film on the catalytic metal layer;
heating the amorphous silicon thin film to monocrystallize the amorphous silicon thin film, thereby converting the amorphous silicon thin film to a crystalline silicon thin film;
joining the crystalline silicon semiconductor substrate, provided with the crystalline silicon thin film, to a support substrate so that the crystalline silicon thin film faces the support substrate; and
separating and removing the crystalline silicon semiconductor substrate, together with the porous silicon layer, which is the crystalline silicon semiconductor substrate in its portion converted to a porous layer, from the crystalline silicon thin film joined to the support substrate.
[2] The process according to the above item [1], wherein the porous silicon layer comprises two or more porous layers having different pore diameters and the porous layer having a larger pore diameter is used as a release layer for separating the crystalline silicon semiconductor substrate from crystalline silicon thin film.
[3] The process according to the above item [1] or [2], wherein the porous silicon layer is formed by anodic conversion.
[4] The process according to any one of the above items [1] to [3], wherein the amorphous silicon thin film is an n- or p-conductivity type layer such that the conductivity type and/or concentration profile are varied in the thicknesswise direction of the layer.
[5] The process according to any one of the above items [1] to [4], wherein the crystalline silicon thin film is joined to the support substrate by anodic joining.
[6] The process according to any one of the above items [1] to [5], wherein an insulating layer is formed on any one of the crystalline silicon thin film and the support substrate and the crystalline silicon thin film is joined to the support substrate through the insulating layer.
[7] The process according to any one of the above items [1] to [6], wherein the catalytic metal layer comprises at least one element selected from the group consisting of nickel, iron, cobalt, platinum, copper, and gold, either as a simple substance or as a compound thereof.
[8] The process according to any one of the above items [1] to [7], wherein the catalytic metal layer has a multi-layer structure comprising an adherent metal layer and a reactive metal layer.
[9] The process according to the above item [8], wherein the adherent metal layer comprises at least one element selected from the group consisting of titanium, chromium, molybdenum, tungsten, and tantalum, either as a simple substance or as a compound thereof.
[10] The process according to the above item [8] or [9], wherein the reactive metal layer comprises at least one element selected from the group consisting of nickel, iron, cobalt, platinum, copper, and gold, either as a simple substance or as a compound thereof.
[11] A process for producing a crystalline silicon thin film, comprising the steps of:
rendering at least a part of the surface of a crystalline silicon semiconductor substrate porous to convert at least a part of the surface of the crystalline silicon semiconductor substrate to a porous silicon layer;
introducing amorphous silicon into pores of the porous silicon layer at least on its surface side to form an amorphous silicon-containing layer:
forming a catalytic metal layer on the amorphous silicon-containing layer:
heating the amorphous silicon contained in the amorphous silicon-containing layer to monocrystallize the amorphous silicon, thereby converting the amorphous silicon-containing layer to a crystalline silicon thin film;
joining the crystalline silicon semiconductor substrate, provided with the crystalline silicon thin film, to a support substrate so that the crystalline silicon thin film faces the support substrate; and
separating and removing the crystalline silicon semiconductor substrate, together with the porous silicon layer, which is the crystalline silicon semiconductor substrate in its portion converted to a porous layer, from the crystalline silicon thin film joined to the support substrate.
[12] The process according to the above item [11], wherein the porous silicon layer comprises two or more porous layers having different pore diameters and the porous layer having a larger pore diameter is used as a release layer for separating the crystalline silicon semiconductor substrate from crystalline silicon thin film.
[13] The process according to the above item [11] or [12], wherein the porous silicon layer is formed by anodic conversion.
[14] The process according to any one of the above items [11] to [13], wherein the amorphous silicon thin film is an n- or p-conductivity type layer such that the conductivity type and/or concentration profile are varied in the thicknesswise direction of the layer.
[15] The process according to any one of the above items [11] to [14], wherein the crystalline silicon thin film is joined to the support substrate by anodic joining.
[16] The process according to any one of the above items [11] to [15] wherein an insulating layer is formed on any one of the crystalline silicon thin film and the support substrate and the crystalline silicon thin film is joined to the support substrate through the insulating layer.
[17] The process according to any one of the above items [11] to [16], wherein the catalytic metal layer comprises at least one element selected from the group consisting of nickel, iron, cobalt, platinum, copper, and gold, either as a simple substance or as a compound thereof.
[18] The process according to any one of the above items [11] to [17], wherein the catalytic metal layer has a multi-layer structure comprising an adherent metal layer and a reactive metal layer.
[19] The process according to the above item [18], wherein the adherent metal layer comprises at least one element selected from the group consisting of titanium, chromium, molybdenum, tungsten, and tantalum, either as a simple substance or as a compound thereof.
[20] The process according to the above item [18] or [19], wherein the reactive metal layer comprises at least one element selected from the group consisting of nickel, iron, cobalt, platinum, copper, and gold, either as a simple substance or as a compound thereof.